Finishing Monoblock with Optimised Transmission Ratio for a Billet Rolling Plant

ABSTRACT

A finishing monoblock with optimised transmission ratio for a billet rolling plant comprises a plurality of rolling stands (G 1 -Gn) arranged in sequence suitable for forming a rolling line and actuated by a pair of mechanical transmissions ( 11, 12 ) in which bevel gear pairs are foreseen for the variation of ratio in the stands of the rotation speed of rolling cylinders ( 18 ). According to the invention, such a variation of the ratio in the stands is carried out through the combination of a first type (A, B) of bevel gear pairs with a second type of bevel gear pairs (C, D) and there is a set of four of cylindrical gears suitable for making four stands (C, D) with the same transmission bevel gear pair.

The present invention refers to a finishing monoblock with optimised transmission ratio for a billet rolling plant.

In a rolling plant or rolling mill for billets, according to established technology, a billet previously taken to a temperature of over 1000° C. is operated upon to then subject it to rolling so as to gradually reduce its section to the desired size. In the production of high-quality and special steel wire rods, high mechanical characteristics, elastic limit and deformability in drawing are parameters of particular importance.

In a rolling mill, one of the critical sections thus consists of the finishing monoblock that, through a plurality of rolling stands, reduces the size of the billet producing the wire rod to be sent to the calibrator or directly to the laying head.

To give the wire rod a circular section or in general a regular profile, the rolling rings or cylinders of the rolling stands are arranged alternately staggered for example by 90 degrees, so as to roll different zones of the billet.

In current machines an assembly combination of the rolling cylinders is used to produce different diameters of wire rod, normally starting from the larger sizes to then continue with the subsequent stands, up to the predetermined diameter.

Since the mass of product going in and the mass of product going out must necessarily be identical, during rolling there is an increase in linear speed of the billet to compensate for the reduction in section that involves an increase in length thereof.

The cylinders in the various stands therefore generally rotate at different speeds increasing from the first to the last.

In order to obtain the variation in ratio between the stands, commanded in succession by two transmissions, one normally acts upon the bevel gear pair.

In this way, it becomes necessary to have the slowest cage (the first of the series) with a very high transmission ratio to reduce on the bevel gear pair and the fastest cage (the last of the series) with a very high ratio to multiply.

The total ratio, for a monoblock of ten stands, is valued at about equal to 5.6406254 to be carried out through groups of two stands with five different bevel gear pairs.

For eight stands the aforementioned ratio is, on the other hand, about equal to 3.6627 to be carried out through groups of two stands with four different bevel gear pairs.

These conditions require large, expensive bevel gear pairs, which given their very high transmission ratio, cause very large reactions on the bearings, meaning that very large bearings must be chosen to support the loads.

However, large bearings have speed limitations.

Alternatively, small bearings can be used to withstand the high speed but they have the drawback of a short lifetime and therefore require frequent maintenance. The variations in transmission ratio carried out through bevel gear pairs as described above also generate the need to have a bevel gear pair with dedicated ratio for each pair of stands with consequent high costs for the spare parts and consequent sizing of other parts of the stands involving both high construction costs and high costs for spares to be kept in stock.

The general purpose of the present invention is, therefore, that of providing a finishing monoblock with optimised transmission ratio for a billet rolling plant.

Another purpose of the present invention is that of providing a finishing monoblock with optimised transmission ratio that allows the reduction of the stocks of spare parts to be kept in storage.

In view of the aforementioned purposes, according to the present invention, it has been thought of to make a finishing monoblock with optimised transmission ratio, having the characteristics outlined in the attached claims.

The structural and functional characteristics of the present invention as well as its advantages compared to the prior art shall become even clearer from an examination of the following description, referring to the attached schematic drawings, in which:

FIG. 1 is a schematic view of a finishing monoblock with ten stands for billet rolling plants according to the invention;

FIG. 2 is a schematic view of a finishing monoblock with eight stands for billet rolling plants according to the invention.

With reference to the figures, a monoblock 10 is schematically illustrated in FIGS. 1 and 2 and has ten and eight stands, respectively.

The rolling monoblock 10 comprises two parallel mechanical transmissions, a first transmission 11 and a second transmission 12, connected through a command reducer 13 in turn connected through gears to a work driving motor.

The mechanical transmissions are equipped with pairs of conical gears A, B, C, D and with gears 17 that transmit the rotation in cascade to the rolling cylinders 18 of the various stands G1, G2, . . . , Gn of the rolling monoblock 10.

In the illustrated examples such a monoblock respectively foresees ten rolling stands G1-G10 (FIG. 1) or eight rolling stands G1-G8 (FIG. 2) in succession, commanded alternately through the two transmissions 11 and 12, so that the first transmission 11 commands the odd stands G1, G3, . . . , G9 (or else G7) whereas the second transmission 12 commands the even stands, G2, G4, . . . , G10 (or else G8).

The transmission according to the invention is made through the combination of a first type A, B of bevel gear pairs with a second type of bevel gear pairs C, D, by inserting a ratio into the cage exploiting the set of four zones 17, with a different ratio from the set of four 19, so that such a ratio is different between the stands and capable of creating a reduction by themselves so as to eliminate a reduction in size of the bevel gear pair to obtain four stands with the same bevel gear pair.

In such a way the ratio between the first bevel gear pairs to reduce and the last bevel gear pair to multiply reduces substantially.

The total ratio for ten stands in the solution according to the present invention is equal to 5.6907497 from which one takes a ratio given by the sets of four and equal to 1.5454545 so that it remains for the bevel gear pairs to distribute a ratio of just 3.6822498 to be carried out in groups of two only on four groups instead of five as in the stands according to the prior art.

Indeed, the differentiation of the set of four provides for a group of two stands, having optimised the intermediate stands with a ratio very close to 1:1 (to be precise 1.244898 and 0.8032786).

The pairs thus made cause very small axial thrusts. The same bevel gear pair with ratio 1.244898 is used keeping it at the contrary on the group of the two subsequent stands without inverting the helix so that 1/1.244898 corresponds to 0.8032786 thus obtaining the same bevel gear pair for six whole stands.

The problem of the very high ratio is also solved by consequently decreasing the reactions on the bearings, since from the ratio value of the machine according to the prior art, at the ends of 2.375 and 0.4210526 it has passed to a ratio of 1.9189189 and 0.5211267.

Through such differentiation it is possible to use small bearings suitable for the high speeds ensuring a longer lifetime.

Moreover, for the ten machines only two types of bevel gear pairs are sufficient, instead of the five before, substantially reducing the construction costs and spare part costs to be kept in stock.

As far as the monoblock comprising eight stands is concerned, the total of the ratio with the new proposed solution is 3.682249 from which a ratio given by the sets of four again of 1.5454545 is taken, with it remaining for the bevel gear pairs to distribute just a ratio of 2.965602, to be carried out in groups of two only on three groups instead of four according to the prior art since the differentiation of the sets of four provides for a group of two stands.

In this case the identical bevel gear pairs of the previous ten stands are used eliminating the first with a high ratio and starting with a ratio of 1.244898 instead of 1.9189189.

By inverting the assembly, such a pair remains identical for the second and third group of two stands thus managing to obtain the use of just two types of bevel gear pairs for all eight stands, instead of the four types of bevel gear pairs of the old solution.

It should be highlighted that by thus being able to start at the first stands with a ratio close to 1:1.244898 there are substantially smaller reactions at the bearings and it is even possible either to put a greater load on the stands, or to achieve a significantly longer lifetime of the bearings. This new solution also allows the group of eight stands to reach the same final maximum speed at the eighth cage as at the tenth cage of the previous group of ten stands.

Also in this case the reduction in the number of different stocks, which is the cause of the high cost of spare parts, should be highlighted.

In conclusion, given the substantially smaller number of different stocks the objective of having transmission groups ready in stock that allow, in the case of an emergency or maintenance, the quick replacement of the cage complete with its transmission (bevel gear pair and splitter for set of four), a thing that previously could not even have been proposed since one would have had to have five stands for the group of ten and four stands for the group of eight.

In the monoblock according to the present invention for the group of ten stands four stands suffice and for the group of eight stands three stands suffice.

On the other hand, if one wanted to drastically limit the spare parts, it is possible to just keep in stock the transmission of a single cage with two sets of bearings not assembling the bevel gear pairs, which are only of two types both for the ten and for the eight stands. When problems are discovered in those undergoing processing, after the cage with problems has been identified, the spare cage with the relative bevel gear pair is mounted and it is ensured in a very short space of time that one is ready to replace the possible malfunctioning cage.

From what has been described above with reference to the figures, it is clear how a finishing monoblock for a billet rolling plant according to the invention is particularly useful and advantageous.

The purposes mentioned in the preamble of the description are thus achieved.

Of course, the monoblock according to the invention can be different to the one described and shown just as a non-limiting example in the drawings.

The scope of protection of the invention is therefore defined by the attached claims. 

1. Finishing monoblock with optimised transmission ratio for a billet rolling plant of the type comprising a plurality of rolling stands (G1-Gn) arranged in sequence suitable for forming a rolling line and actuated by a pair of mechanical transmissions (11, 12) in which bevel gear pairs are foreseen for the variation of ratio in the stands of the rotation speed of rolling cylinders (18), characterised in that such a variation of the ratio in the stands is carried out through the combination of a first type (A, B) of bevel gear pairs with a second type of bevel gear pairs (C, D) and in that there is a set of four of cylindrical gears suitable for making four stands (C, D) with the same transmission bevel gear pair.
 2. Finishing monoblock with optimised transmission ratio according to claim 1, characterised in that the total transmission ratio for a monoblock of ten stands (G1-G10) is equal to 5.6907497 from which one takes a ratio given by the difference between the ratios of the sets of four and equal to 1.5454545 so that a ratio of just 3.6822498 remains to be distributed.
 3. Finishing monoblock with optimised transmission ratio according to claim 1, characterised in that the differentiation of the set of four provides for a group of two stands, having optimised the intermediate stands with a ratio very close to 1:1, preferably close to 1.244898 and close to 0.8032786.
 4. Finishing monoblock according to claim 1, characterised in that the total transmission ratio for a monoblock of eight stands (G1-G8) is close to 682249 from which a ratio given by the sets of four close to 1.5454545 is taken, with it remaining for the bevel gear pairs to distribute just a ratio close to 2.965602.
 5. Finishing monoblock according to claim 4, characterised in that the bevel gear pairs remain identical for the second and third group of two stands obtaining the use of just two types of bevel gear pairs for all eight stands, instead of the four types of bevel gear pairs of the old solution.
 6. Finishing monoblock according to claim 1, characterised in that it requires just the transmission of a single cage with two sets of bearings with bevel gear pairs, of two types, as stock. 